1. Field of the Invention
The invention concerns a method for balancing individual channels of a pulse radar system having multi-channel signal evaluation and a radar system using this method.
2. Description of the Prior Art
Radar systems of the above kind are used primarily for tracking. For this purpose, squint signals are generated for azimuth and elevation, which are reduced to zero in free space when the target axis of the antenna is aimed exactly at the target. The subsequent guiding of the antenna for tracking is accomplished by two servo circuits, one for setting the elevation and one for setting the azimuth. Radar systems of this kind are generally known.
If targets are tracked with a radar system of this kind in an area in which, for example, the echo signals are reflected on a water surface in the direction of the antenna, an elevation squint signal occurs, which will not become zero even when the target axis of the antenna is aimed exactly at the target. The result of this water reflection squint signal is that the elevation servo circuit guides the target axis of the antenna away from the target during the subsequent tracking phase of its operation.
To cope with this difficulty, therefore, in the so-called cross-feed method, additional squint signals are used, which, when the combination is right, produce a zero reading on the target axis even when there is reflection. This method is described extensively in Swiss patents Nos. 592,887 and 629,898, incorporated herein by reference. This method requires a so-called cross-channel in the radar device, and in both the elevation and cross-channel signals, there are generated squint components which have both in-phase and quadrature elements. The quadrature elements only occur if, as the result of reflections, the reception signal consists of two echo elements, namely the direct echo and the reflected echo. In this case the phase relation between the two signal components can be arbitrary and is determined by the instantaneous geometric configuration of the overall position. In order to be able to eliminate the effect of the reflected echo, however, the amplitude and the phase of the elevation and cross signals, as well as the sum signal that is required for the signal processing, must be transmitted error-free through the antenna and the reception channels to the Doppler evaluation circuit of the radar device. Deviations from these conditions would result in false squint components, which can make the use of the crossfeed method a questionable procedure.
Therefore, to avoid asymmetries of magnitude and phase in the reception channels, calibrations are made at regular time intervals, both when a radar device of this kind is initially turned on and when it is in stand-by operation. Errors resulting from deviations of the antenna from its ideal form can be detected on the antenna test position and retained in the radar device as correction values, which are then taken into account when the squint signals are processed. During the calibration, a test signal is entered either in the antenna or in its radio frequency feed lines.